Medical ultrasound images have noises and artifacts. Various techniques have been developed and utilized to reduce noise and improve image quality.
For example, U.S. Pat. No. 5,632,277 discloses an ultrasound imaging system employing phase inversion subtraction to enhance the image generated, in which first and second amplitude modulated harmonic ultrasound signals that differ by 180 degrees in phase are transmitted to generate echo signals that are measured and combined to form ultrasound images. U.S. Pat. Nos. 6,866,631, 7,226,416, and 7,699,781 disclose variations of phase inversion ultrasonic imaging using multiple sets of transmit pulses differing in amplitude, frequency, phase, and/or pulse width.
U.S. Pat. Nos. 5,740,128, 5,833,614, and 5,913,823 disclose ultrasonic harmonic imaging systems in which ultrasonic energy is transmitted at a fundamental frequency and reflected ultrasonic energy is received at a harmonic of the fundamental frequency. In U.S. Pat. Nos. 5,740,128 and 5,913,823, ultrasonic energy is transmitted in power bursts, each having a respective envelope shape rising gradually to a respective maximum value and fall gradually from the respective maximum value. In U.S. Pat. No. 5,833,614, pulses of different durations are used.
U.S. Pat. No. 5,980,459 disclosed a technology that utilizes phase-coded pulses and slow-time filtering to obtain harmonic signals.
In order to improve harmonic imaging performance, other ultrasound methods like compounding are added to the harmonic imaging mode. For example, U.S. Pat. Nos. 5,897,500 and 6,458,083 disclose combining both fundamental and harmonic signals to form a compounded image.
The entire disclosures of the above discussed U.S. patents related to harmonic imaging techniques are hereby incorporated herein by reference.
Although some of the methods are effective in improving image qualities, they may introduce drawbacks in other areas. For instance, most current Tissue Harmonic Imaging (THI) techniques have drawbacks in penetration loss and frame rate reduction.